# Questions tagged [optics]

Optics is the study of light, and its interaction with matter. It includes topics such as imaging systems, fiber optics, lasers, quantum optics, and more.

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### I have found a serious error in a Wikipedia page? [duplicate]

From WP Signal Velocity article: https://en.wikipedia.org/wiki/Signal_velocity Signal velocity is usually equal to group velocity (the speed of a short "pulse" or of a wave-packet's middle ...
65 views

### Units make speed of light dimensionless..?

We shall now adopt a new unit for time, the meter. One meter of time is the time it takes for light to travel one meter ... (page-4, Bernhard Schutz's A first course in relativity) I am confused, how ...
33 views

### Can we apply lens makers formula when medium on both side of lens is different? [closed]

A symmetric biconvex lens of radius of curvature $R$ and made of glass of refractive index $1.5$, is place on a layer of liquid placed on top of a plane mirror as shown in the figure. An optical ...
48 views

### How does a rainbow show all of its colours?

My question is tied closely to this one, asked a while back on the website. As far as my understanding goes, a rainbow is formed by sunlight undergoing two refractions and a reflection inside ...
5 views

### Is it possible that the rotating Doppler signal disappears at a certain degree of coherence?

Using the superposition state of the ±m LG mode to detect the rotational Doppler effect of partially coherent light, is it possible that when the coherence reaches a certain value, the rotational ...
14 views

### Clarifications about units of Photon Flux (PF) and Photon Flux Density (PFD)

I have an emitting source of light (this LED - Light Emitting Diode, UO variant). On page 5 I read the minimum PF Photon Flux is ...
36 views

### Phase-amplitude decomposition of a wave

Consider the stationary Schrodinger equation in 1D: $$\psi''(x) + Q(x) \psi(x) = 0 \quad x \in [0, L]$$ I am specifically interested in the case where $Q(x)$ is monotonic and gives a single turning ...
46 views

### Are laser diffuse reflections really so dangerous?

Class IV lasers are lasers with an optical power higher than 500mW, and for these lasers "even diffuse reflections can cause permanent eye damage". Well, I would like to understand how this ...
23 views

### Finding Shift due to Refraction in Multiple Slabs when the object and viewer are in different medium [duplicate]

So, suppose we have three rectangular slabs each of varying refractive indices(R.I.) and thickness. We have a real point object to the left of the first slab and we have an observer to the right of ...
33 views

### Phase shift measurement calculation problem [closed]

I hope this is the correct site for this post. I am interested in mobile robotics and now I'm learning about its sensors.I have come across a problem where I need to calculate the distance of the ...
29 views

### What lenses are generally used to focus a beam of light into a horizontal line?

I am trying to find out more about the inner workings of a laser scanner I'm using to map objects. In this case the technical details are quite hard to come by. The laser scanner generates a beam of ...
28 views

### Difference-frequency-generated (DFG) spectral width

If we have two laser beams with central wavelengths $\lambda_1$ and $\lambda_2$, (one with a spectral width of $\Delta\lambda_2$ and one with negligible spectral width), interacting in a non-linear ...
40 views

### Can we tell on which side of a lens an image appears?

Suppose I look through a single, thin, converging lens at an object on the opposite side. Depending on where the object is placed, the lens will either produce a real image on the side of the lens ...
16 views

### Sources about $M^2$ parameter for lasers

I am trying to find some sources about the $M^2$ parameter for lasers, I have already looked for that in 3 of the following books: laser-electronics-prentice-hall-1995 OrazioSvelto PrinciplesOfLasers ...
20 views

### Does the speed of an object underwater change when viewed above?

Let's say a submarine is coming to surface with a velocity $v$ normal to the surface of water and let's say you are the admiral of the navy viewing the submarine from the top. The submarine is exactly ...
8 views

### Validity of defining Effective Permittivity in Dielectric Mixture

I am a optics-major student currently studying the topic of line-of-sight propagation of wave in scattering medium. I recently noticed some interesting articles about microwave propagation in mixtures,...
6 views

### Development of the incident light transfer matrix on a multilayer structure

I am trying to read an article whose objective is to simulate a DBR (Distributed Bragg Reflector), however I do not understand very well why the matrix that represents the change that light undergoes ...
23 views

### Refraction and Shift in multiple glass slabs [closed]

So, suppose we have three rectangular slabs each of varying refractive indices(R.I.) and thickness. We have a real point object to the left of the first slab and we have an observer to the right of ...
1 vote
76 views

### How do retinal cones see color when the cones pickup photons and not waves?

I am wondering how cones (photoreceptors in the retina) can see color if colors are wavelengths but cones send signals when they absorb photons. Maybe by using the energy level (or only being ...
48 views

### How can conservation of etendue be explained geometrically?

I have tried to understand the principle of conservation of etendue, more specifically the limit on concentration, but when I try to reproduce it with this simulator it doesn't seem to work. The angle ...
21 views

### Intensity of Single Slit Diffraction

I'm currently trying to derive the intensity pattern for a single slit diffraction. In this website (in Spanish) its said that the amplitude can be given as the length of a line and the original ...
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### Different wave speeds when considering direction of electric or magnetic field in birefrigent materials

Let us consider a linear birefringent material which is not isotropic and has three principal axes with refractive indices $n_1$, $n_2$ and $n_3$ for the $x$, $y$ and $z$ directions, respectively (we ...
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### Sign Convention in Ray Optics

While solving questions on Refraction due to 2 spherical surfaces the sign of the image formed after the first refraction (here at '$A$') depends whether the image formed is towards left or right side ...
1 vote
34 views

### Non-parallel light diffraction

Does light (and in general any kind of wave) diffract only when the wave fronts are parallel? Like if you did the double slit experiment when the waves were coming from a point source close to the ...
48 views

### How is this circular pattern of a streetlantarn behind a tree formed?

A few months ago, while walking the dog at night, I noticed a strange effect. The streetlight shining behind a barren winter tree, was somehow changed, by reflection from the branches, showed a ...
1 vote
60 views

### What kind of lense do you need to use to get a picture of the sun that looks like this?

This is a picture of the sun from the moon. When I look at the sun with my eyes, I see something like this: But the above picture is perfectly round, which makes me think it has to do with the shape ...
50 views

### Do prescribed glasses transmit light? [closed]

If prescribed glasses can transmit light, what percentage of light can it transmit.
49 views

### Geometric optics explanation of lateral (transverse) chromatic aberration

The majority of pictures explaining lateral(transverse) chromatic aberration look like this Here the focal point for red light is shifted closer to the optical axis and the focal point for blue light ...
50 views

### Path of ray of light through a stack of lenses [closed]

The given question is as follows there are a large number of thin lenses all with focal length f separated by a distance l with their optical axes coinciding a ray starts at a height h parallel to the ...
23 views

### Why is the angle of incidence equal to angle of reflection? [duplicate]

This is true experimentally, but how do I prove this?
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### Mirror Equation for convex mirror

Question: I have a convex lens with focal length $\mathrm{70mm}$ and it's forming a real image. We have a virtual object at $\mathrm{90mm}$ to the right of the mirror. Using the mirror equation gives ...
95 views

### What is the wavelength of light in a practical sense?

Okay, so I know that a wavelength is a distance of crest and a trough added together which makes a whole wave, but what is it in the real sense? Like in the case of sound I know when we say "...
71 views

### Why image of vertical object is always a straight line and perpendicular to principal axis?

I am a high school student and I am very confused in geometrical optics, In all textbooks the mirror formula is derived by already assuming that the image of any vertical object (perpendicular to the ...
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### Lens and plane mirror [closed]

What is the proof for focal length of this combination being equal to half of convex lens? I tried with equivalent focal length formula but then feq = f itself as the focal length of plane mirror is ...
48 views

### Concave mirror and convex mirror placed facing each other [closed]

A convex mirror in a concave mirror each of focal length f are placed coaxially. They are separated by 4f and their reflecting surfaces face each other. A point object is kept on the principle axis at ...
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### I have been told that in an xyz plane.The normal on incident point is given,how do I visualise a normal which is like this

Suppose I have a ray of light incident on a plane mirror in the general form of $$ai+bj-ck$$. I have a normal that is along $$\frac{i+j}{√2}$$. The question asks me to find the unit vector but that is ...
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### The meaning of Y in sRGB color space [closed]

In the definition of sRGB color space, https://en.wikipedia.org/wiki/SRGB Is the Y relative luminance in the above table？ What does the value of Y equal to 1 for white point mean? The chromaticity ...
44 views

### Two coherent state input to a beam splitter

A beam splitter transforms incoming mode operators $\hat{a}_{i}, \hat{b}_{i}$ to outgoing operators $\hat{a}_{o}, \hat{b}_{o}$ as  \begin{aligned} &\hat{a}_{o}=\sqrt{\eta} \hat{a}_{i}+i \sqrt{1-\...
15 views

### Conversion of energy to power in a cavity

Suppose I have a cavity and I fill it up with photons. Let's assume the cavity is in steady state. Multiplying the number of photons with the photon energy gives me the total energy stored inside the ...
1 vote
50 views

### Interference and diffraction pattern without lens

There is a slight conflict going on in my various physics books regarding the apparatus of Young double slit experiment and single slit diffraction. In some books they have written that a lens must be ...
16 views

### Diode laser optics - How to shape the beam of a Diode bar?

I have a 40w, 808nm, CS mount diode bar. I would like to build a something similar to a Rofin Dilas laser diode. How to choose the optics, measure distance, focus the beam into a fiber coupler? I came ...
15 views

### How to add markers to IR photographs

I'm using an IR camera to identify thermal patterns. The thermal images are similar to this [LINK] image. I'd like to add markers to the area being measured to determine dimensions and normalize the ...
1 vote
32 views

### Does light intensity affect transparency

The reason for the transparent nature of glass is that the photons of visible light don't have enough energy for the electrons of glass to absorb and jump to higher energy levels. As a result, the ...
1 vote
16 views

### Wavefront of a cylindrical beam of light

The given question states that a cylindrical beam of light with refractive index of the beam varying as u=A+B/r^2 where r is the distance form the axis of the beam. Now the questions asks us the shape ...
1 vote
38 views

### Number of Fringes obtained on Interference of Lights of different Wavelengths

The Question goes as follows: I am stuck at the part where we obtain General Equation for Path Difference of two Interfering Lights. Since Wavelength of those Interfering Lights are different, so I ...
38 views

### Image formation from refraction through a water surface (plane diopter)

Let's suppose that an object sits in water. The light rays comings from that object will get refracted at the water surface at different angles and the refracted rays are not concurrent (do not meet ...
45 views

### How differential wave equation is in general? [closed]

How the differential wave equation is in general? While deriving the equation it is assumed that wave maintains constant shape and constant velocity. Then how can it be a general wave equation as the ...
13 views

### How to calculate the minimum distance where a USB cam provides sharp footage?

Can one calculate the minimum distance for a USB cam at which images appear sharp only from the focal length. Let's take this webcam from elpcctv as example. The focal length is 2.8mm and the sensor ...